Encoder, decoder and methods thereof

Abstract

An encoder whereby the bit efficiency of encoding can be improved, thereby improving the qualities of signals as decoded. In the encoder: a time-frequency converting unit ( 101 ) converts signals, which are to be encoded, to frequency domain signals; an adaptive spectrum formation encoding unit ( 102 ) determines an effective range in the frequency band of the frequency domain signals; and a pulse vector encoding unit ( 103 ) pulse vector encodes only the signal components within the effective range.

The invention claimed is: 
     
       1. An encoder comprising:
 a time-frequency conversion section that converts a coding target signal into a frequency domain signal; 
 an effective range specifying section that specifies an effective range in a frequency band of the frequency domain signal; and 
 a pulse vector coding section that performs pulse vector coding on only a signal component within the effective range. 
 
     
     
       2. The encoder according to  claim 1 , wherein the effective range specifying section comprises:
 a spectrum specifying section that specifies a plurality of spectrum coefficients in descending order of an amplitude absolute value in the frequency domain signal; 
 a minimum position specifying section that detects a minimum frequency of frequency positions of the plurality of spectrum coefficients, as a starting point of the effective range; and 
 a maximum position specifying section that detects a maximum frequency of frequency positions of the plurality of spectrum coefficients, as an end point of the effective range. 
 
     
     
       3. The encoder according to  claim 2 , wherein the minimum position specifying section and the maximum position specifying section detect the minimum frequency and the maximum frequency by storing positions of the plurality of spectrum coefficients in a sequence and sorting the sequence. 
     
     
       4. The encoder according to  claim 2 , wherein the effective range specifying section outputs the minimum frequency and the maximum frequency as effective range information. 
     
     
       5. The encoder according to  claim 1 , wherein the effective range specifying section determines whether or not the frequency band is within an effective range, for each of a plurality of divided subbands. 
     
     
       6. The encoder according to  claim 1 , wherein the effective range specifying section comprises:
 a standard value specifying section that specifies a specific order spectrum coefficient in descending order of an amplitude absolute value in the frequency domain signal, as a standard value; 
 a dividing section that divides the frequency domain signal for each of a plurality of subbands into which the frequency band is divided, and acquires a subband signal; 
 a detecting section that detects spectrum coefficients in which an amplitude absolute value is maximum, for each subband acquired in the dividing section; and 
 a determination section that determines whether or not a subband in which the detected spectrum coefficient is present is within an effective range, by comparing the detected spectrum coefficient with the standard value. 
 
     
     
       7. The encoder according to  claim 1 , wherein the effective range specifying comprises:
 a standard value specifying section that specifies a specific order spectrum coefficient in descending order of an amplitude absolute value in the frequency domain signal, as a standard value; 
 a signal classification section that classifies signal characteristics of the coding target signal; 
 a dividing section that divides the frequency domain signal for each of a plurality of subbands into which the frequency band is divided, and acquires a subband signal; 
 a weighting section that multiplies each of a plurality of subband signals acquired in the dividing section by weight according to the classified signal characteristics; 
 a detecting section that detects spectrum coefficients in which an amplitude absolute value is maximum, for each of the weighted subband signal; and 
 a determination section that determines whether or not a subband in which the detected spectrum coefficient is present is within an effective range, by comparing the detected spectrum coefficient with the standard value. 
 
     
     
       8. The encoder, according to  claim 5 , wherein the effective range specifying section outputs a flag signal showing a subband determined to be within an effective range, as effective range information. 
     
     
       9. A decoder comprising:
 a pulse vector decoding section that performs pulse vector decoding on a pulse coding parameter coded in the encoder according to  claim 1 ;
 a spectrum forming section that arranges a decoded signal acquired in the pulse vector decoding section in a band corresponding to the effective range; and 
 a frequency-time conversion section that converts a decoded signal arranged in the band corresponding to the effective range into a time domain signal. 
 
 
     
     
       10. A coding method comprising :
 a step of converting a coding target signal into a frequency domain signal; 
 a step of specifying an effective range in a frequency band of the frequency domain signal; and 
 a step of performing pulse vector coding on only a signal component within the effective range. 
 
     
     
       11. A decoding method comprising:
 a decoding step of performing pulse vector decoding on a pulse coding parameter coded in the coding method according to  claim 10 ; 
 a spectrum forming step of arranging a decoded signal acquired in the decoding step, in a band corresponding to the effective range; and 
 a converting step of converting a decoded signal arranged in the band corresponding to the effective range into a time domain signal.